1. Field of the Invention
This invention relates to a composite material for sliding surface bearings, comprising a supporting shell of steel, which is covered by a bearing metal layer comprising sintered porous bronze, which has a porosity of 25 to 45% and the voids of which are filled with a fluorocarbon-lead mixture and which is covered by an antifriction layer comprising the fluorocarbon-lead mixture in a thickness of 30 to 500 microns.
2. Discussion of Prior Art
In such a composite material for sliding surface bearings, a copper-plated or non-copper-plated steel backing is provided with a sinter-bonded layer, which has a thickness of 250 to 350 microns and has been made from spherical, nodular or irregularly shaped tin bronze powder having a particle size of 150 to 175 microns. The porous bronze layer has a porosity of 35 to 45% and its voids have been entirely filled in a rolling operation with a mixture of polytetrefluoroethylene, e.g., in a quantity of 80% by volume, and lead powder, e.g., in a quantity of 20% by volume. The bronze layer is covered with an anti-friction layer, which consists of the polytetrafluoroethylene-lead mixture in a thickness of 10 to 30 microns. That mixture has been sintered out. Owing to the steel backing and the porous bronze layer that composite sliding surface bearing has a high compressive strength and a high thermal conductivity (Machinenmarkt/MM-Industriejournal 77, No. 6, of Jan. 19, 1971, "Lager ohne Ol). It is also known to use polyacetal rather than polytetrafluoroethylene in such composite material for sliding surface bearings (VDI-Z. 110 (1968), No. 15, pages 632 to 636).
Said composite materials for sliding surface bearings have the disadvantage that the anti-friction surface must not be machined by lapping or shaving because the machining might destroy the anti-friction layer, which is important for the function of the bearing.
In view of developments in modern mechanical engineering, sliding surface bearings are desired which meet the increased requirements. From this aspect it is an object of the present invention to provide for sliding surface bearings a composite material which in its mechanical technological behavior in operation is at least equivalent to conventional composite materials for sliding surface bearings but which has an anti-friction surface which can be machined-particularly to form the anti-friction surface with pockets or grooves for receiving lubricant.